A vane rotary expander is a kind of displacement type fluid machinery, of which basic structure is disclosed in, for example, Japanese Patent Laid-Open Publication No. 57-210101.
Now, the configuration of the vane rotary expander will be described below. FIG. 4 is a transverse sectional view showing a conventional vane rotary expander. The reference numeral 1 denotes a cylinder having a cylindrical inner wall 1a. The cylinder 1 has side plates (not illustrated in the figure) disposed at its both ends. Inside of the cylinder 1, a cylindrical rotor 3 is disposed, and an outer circumferential segment of the cylindrical rotor 3 defines a small clearance 2 together with the inner wall 1a of the cylinder 1. The rotor 3 has grooves 3a formed perpendicularly to its top and bottom end surfaces at an interval of 90 degrees. Vanes 4 are inserted into the grooves 3 at the respective ends thereof so as to be freely slidable, and the other ends of the vanes 4 are in contact with the inner wall 1a of the cylinder 1. An operating chamber 5 is formed at spaces 5a, 5b, 5c, 5d, and 5e surrounded by the inner wall 1a of the cylinder 1, the rotor 3, and the vanes 4. A shaft 6 formed integrally with the rotor 3 is rotatably supported by means of an axis. The cylinder 1 has an intake 7, through which an operating fluid is forced to flow into the operating chamber 5, and a discharge port 8, through which the operating fluid is forced to discharge from the operating chamber 5. Note that the discharge port 8 has an opening portion 8a, which opens within a given circumferential range on the inner wall 1a of the cylinder 1. Assuming that the number of the vanes 4 is n, the range, where the opening portion 8a is formed, starts at a position of {180×(1+1/n)} degrees from the small clearance 2 in the direction where the shaft 6 rotates indicated by an arrow in the figure and ends at a position in the vicinity of the small clearance 2. Note that in FIG. 4, the range of the opening 8a starts at a point of 225 degrees from the small clearance 2 because the number of the vanes 4 is four. On the side of the cylinder 1, a cover 9 is attached, inside of which a suction channel 10 for guiding the operating fluid into the intake 7, a discharge chamber 11 for temporarily storing the operating fluid flowing out from the discharge port 8, and a discharge channel 12 for discharging the operating fluid out from the discharge chamber are formed.
Now, focusing on the operating chamber 5, the operation principle of the vane rotary expander will be described below. Initially, the operating chamber is generated in the space 5a on the intake 7 side of the small clearance 2. Then, as the rotor 3 rotates, the operating chamber 5 performs a process for sucking the operating fluid from the intake 7 under a pressure Ps on the high-pressure side while increasing its volume, namely a suction process. As soon as the operating chamber 5 reaches the space 5b, a communication to the intake 7 is shut off, forming an enclosed space. Thereafter, the operating chamber 5 performs a process for depressurizing the operating fluid contained therein while increasing its volume as the rotor 3 rotates, namely an expansion process. The operating chamber 5 communicates to the opening portion 8a of the discharge port 8 immediately after reaching its maximum volume in the space 5c. Then, the operating chamber 5 performs a process for discharging the operating fluid into the discharge chamber 11 through the discharge port 8 while decreasing its volume as the rotor 3 rotates, namely a discharging process.
The vane rotary expander rotates the rotor 3 by means of a force exerted on the vane 4, which is generated using a difference in pressure between two adjacent operating chambers 5, while the operating fluid expands and a pressure thereof is depressurized in the expansion process to obtain the power for rotating the shaft 6 integrally formed with the rotor 3.
In the case of a conventional vane rotary expander having the above-mentioned structure, the volume of sucked fluid is equal to the volume Vb of the space 5b, where the operating chamber 5 is situated immediately after the suction process ends and the volume of discharged fluid is equal to the volume Vc of the space 5c, where the operating chamber 5 is situated immediately before the discharging process begins. Since Vb and Vc are specific to the expanders, a volume ratio (Vb/Vc) remains constant. Assuming that the adiabatic coefficient of the operating fluid is κ, the pressure applied to the space 5c, where the operating chamber 5 is situated immediately before the discharging process, is Pc, and the pressure applied to the space 5b, where the operating chamber 5 is situated immediately after the suction process, is Ps, the following relational equation (1) is established.Pc=Ps×(Vb/Vc)κ  (1)
The pressure Pc applied to the space immediately before the discharging process can be found by assigning values to the suction pressure Ps, which is a pressure at the inlet of the expander, and to the volume ratio Vb/Vc, respectively, from the above equation. Since the pressure Pd on the low-pressure side at the outlet of the expander, however, does not always remain constant because it depends on a system where the expander is incorporated. Accordingly, it is assumed that in addition to complete expansion (Pc=Pd), incomplete expansion (Pc>Pd) or overexpansion (Pc<Pd) may occur. FIGS. 5A and 5B are graphs illustrating the P-V relationship for the operating chamber 5. FIG. 5A is a graph illustrating en example of incomplete expansion (Pc>Pd) and FIG. 5B is a graph showing an example of overexpansion (Pc<Pd).
With reference to FIG. 5A, the/example of incomplete expansion (Pc>Pd) will be described below. In the suction process represented by an A-B line in FIG. 5A, the operating chamber 5 sucks the operating fluid through the intake 7 while increasing its volume up to Vb under the suction pressure Ps. In the expansion process represented by a B-C line, the volume of the operating fluid contained in the operating chamber 5 adiabatically expands up to Vc under the pressure Pc. At a point C, the operating chamber 5 is situated in the space 5c as shown in FIG. 4 and communicates to the opening portion 8a of the discharge port 8 as soon as the rotor 3 rotates by a small distance. At that time, the pressure Pc applied to the operating chamber 5 is higher than the pressure Pd applied to the discharge chamber 11 due to incomplete expansion, forcing the operating fluid to flow into the discharge chamber 11 through the discharge port 8. For this reason, the pressure applied to the operating chamber 5 drops from Pc to Pd while the volume of the operating chamber 5 remains constant, namely Vc. This process is represented by a C-F line shown in FIG. 5A. In the discharging process represented by an F-G line, the operating chamber 5 reduces its volume under the discharge pressure Pd. The power obtained by the expander through the processes mentioned above corresponds to an area ABCFG. On the other hand, the power obtained in the complete expansion (Pc=Pd) process, corresponds to an area ABEG. Accordingly, it may be considered that a loss corresponding to an area CEF due to incomplete expansion has occurred in the expander.
Now, with reference to FIG. 5B, an example of overexpansion (Pc<Pd) will be described below. In the suction process represented by the A-B line, the operating chamber 5 sucks the operating fluid through the intake 7 while increasing its volume up to Vb under the suction pressure Ps. In the expansion process represented by the B-C line, the volume of the operating fluid contained in the operating chamber 5 adiabatically expands up to Vc under the pressure Pc. At the point C, the operating chamber 5 is situated in the space 5C as shown in FIG. 4 and communicates to the opening portion 8a of the discharge port 8 as soon as the rotor 3 rotates by a small distance. At that time, the pressure Pc applied to the operating chamber 5 is lower than the pressure Pd applied to the discharge chamber 11 due to overexpansion, forcing the operating fluid to flow back into the operating chamber 5 from the discharge chamber 11 through the discharge port 8. For this reason, the pressure applied to the operating chamber 5 increases from Pc to Pd while the volume of the operating chamber 5 remains constant, namely Vc. This process is represented by a C-H line shown in FIG. 5B. In the discharging process represented by an H-J line, the operating chamber 5 reduces its volume under the discharge pressure Pd. The power obtained by the expander through the suction and expansion processes mentioned above corresponds to an area ABCD. However, since additional power corresponding to an area JHCD is consumed to flow back the operating fluid through overexpansion in the discharging process, the actual power obtained through all the processes is equal to a difference between the powers corresponding to the respective areas ABCD and JHCD. On the other hand, the power obtained in the complete expansion (Pc=Pd) process, corresponds to an area ABIJ. Accordingly, it may be considered that a loss corresponding to an area IHC due to overexpansion has occurred in the expander.
As known from the above descriptions, the conventional vane rotary expanders have a problem in that since a loss due to incomplete expansion or overexpansion is caused because of their volume ratios Vc/Vb being unchanged, they can obtain only the power lower than the power which may be generated by means of the operating fluid in the complete expansion process.
In order to solve the above-mentioned problem involved with the conventional vane rotary expanders, an object of the present invention is to provide a high-efficiency vane rotary expander, wherein a plurality of discharge ports are formed in the circumferential direction on the inner wall of the cylinder and the volume ratio is variable to prevent a loss in power from occurring.